Tube repairs

ABSTRACT

A method of repairing a joint between a tube and a tube plate comprising removing an end portion of the tube and replacing it with a connector explosively welded to the tube and the plate.

The present invention relates to a method and a device for repairing ajoint, particularly but not exclusively a joint between a heat exchangertube and a tube plate.

Prior Art

In the last decade, explosive metal working techniques have been foundparticularly useful in the production of joints between tubes and bodiessuch as tube plates and tube flanges. The joints may be mechanicaljoints, e.g. made by explosive expansion of a tube to engage a tubeplate mechanically and thereby connect the tube to the plate. The jointsmay alternatively be welded; that is the explosive expansion may be socontrolled as to produce a metallurgical bond between the material ofthe tube and the material of the plate or other body. Examples of theformer technique are shown in U.S. Pat. Nos. 3411198, 3426681, 3543370,3562887, and 3939681, and examples of the latter are shown in U.S. Pat.Nos. 3140537, 3364562, 3364561, 3402870, 3409969, 3446047, 3503110,3562897, 3672035, 3698067, 3717925, 3774291, 3868131 and 4003513.

More recently, explosively formed joints have been used to plugleaking/damaged tubes for example as shown in U.S. Pat. Nos. 3491798,3543387, 3555656, 3590877, 3724062, 3785291, 3919940 and 4021907.Obviously plugging of a heat exchanger tube detracts, however slightly,from the performance of the exchanger, and if an excessive number oftubes is plugged off then the exchanger no longer performs its designedfunction.

Explosive tube repair techniques involving expansion of sleeves withintube ends have also been suggested, for example in U.S. Pat. Nos.3781966 and 4028789 and in our own prior U.S. Patent Application Ser.No. 816913 (U.K. Pat. No. 30140/76). The difficulty with such repairtechniques is that they are designed mainly to deal with damage arisingfrom the interior of the tube. Expansion of the tube end as the repairsleeve is expanded within it may cure a leak between the tube and plate.However, this may require a substantial charge to effect the expansionand the resultant shock on adjacent tube joints may create further leakpaths particularly where the original joints were made by simpleexpansion techniques (e.g. roller expansion) or by a technique producinga brittle weld (e.g. some fusion welding techniques).

It has not previously been appreciated that high energy rate techniquessuch as explosive techniques, permit the removal of the end of the tubeoriginally jointed to the other body, and the replacement of the removedpart by a connector jointed to both the tube and the body. This enablesvirtual re-establishment of the original flow path. It is of coursepossible to use a connector to bridge the original joint withoutremoving the old tube end, but this will usually interfere with the flowpath.

It has of course been known for many years that articles can beexplosively joined by joining each to a connector sleeve. Such atechnique was described in U.S. Pat. No. 2367206. However, thistechnique has not previously been applied to the repair of an existingjoint, especially where that joint is between a tube and a tube endpiece, that is a body extending transversely of the tube and having anopening which receives the end of the tube or which is aligned with theend of the tube so that a flow path including the tube bore extendsthrough said opening. The most common tube endpieces are tube-plates,tube headers and tube flanges, but the invention is not limited to theseparticular endpieces.

DESCRIPTION OF THE INVENTION

The invention therefore relates to a method of repairing a joint betweena tube and another body comprising making a first joint between atubular connector and the tube and a second joint between the connectorand the other body.

At least one joint, and preferably both, may be made by a high energyrate technique, preferably explosive. At least one joint, and preferablyboth, may comprise a weld. At least one joint, and preferably both, maybe made by expansion of the connector. Preferably, part of the tube isremoved to receive the connector. Thus the latter may substantiallyre-establish an original surface of the tube, usually its bore, althoughthe re-established surface could be on the exterior of the tube in somecircumstances.

The tube may be associated with an opening in said other body, and inparticular it may extend into that opening. If the tube extendscompletely through a bore in the other body, a portion of the tube maybe removed to expose a surface on the other body to enable formation ofthe second joint with the exposed surface. Where the tube does notextend into the opening, a support may be provided on a surface of thetube opposite to that surface which forms the first joint to support thetube during formation of the joint with the connector. In any event, theconnector preferably extends into said opening. In the preferredembodiment, both joints are made within said opening in said other body.The latter may be an endpiece as defined above.

Preferably the two joints are made substantially simultaneously. Wherethe joints are made by explosives, simultaneous formation of the jointsis facilitated by use of two detonation fronts travelling in oppositedirections from a common initiating means. However, preciselysimultaneous formation of the joints is not essential, and they could beformed successively by a single detonation front travelling through anelongated charge.

The initiating means for the explosive may be a detonator, and thedetonator may provide a charge for forming one of the said joints. Anadditional charge portion may be provided to form the other joint, beingassociated with the detonator so as to be initiated by it in use.

Preferably the connector and at least one of said bodies are so arrangedthat the joint is formed in accordance with our prior U.S. Pat. No.3,503,110, the disclosure of which is hereby incorporated in the presentspecification by reference. That specification describes a joint betweena tube and a tube plate, but it will be apparent that the techniquesdisclosed therein can be applied to formation of a joint between a tubeand a body other than a tube plate.

The invention also provides a connector for use in a method as describedabove and having a first portion which, when located within a generallycylindrical surface defining a bore, will have a tapered annular spacebetween itself and said surface, and a second portion which is arrangedeither so that

(a) when located in a generally cylindrical surface defining a bore, anannular tapered space will be produced between itself and said surface,or

(b) when located in a tapered tubular surface defining a bore, therewill be an annular tapered space between itself and said surface, eachsaid portion being deformable by a high energy rate technique to form ajoint with said surfaces. The high energy rate technique may involve anexplosive, electro-hydraulic or electro-magnetic forming technique.

The arrangement is preferably such that the tapered spaces producedaround said portions will diverge in opposite directions. The connectormay comprise a cylindrical portion to engage the interior of the tubeand at least two frusto-conical portions providing the first and secondportions respectively. The connector preferably has two cylindricalportions separated by a transition part which may also befrusto-conical. Preferably the frusto-conical portions which provide thefirst and second portions respectively each lead into a cylindricalportion at a respective end of the connector.

Preferably the connector has a tubular insert of solid energytransmitting material, preferably polythene. The external surface of theinsert may engage the internal surface of the connector, or an air gapmay be provided between the insert and the connector over at least aportion of their facing surfaces. At least a portion of the internalsurface of the insert may be suitably profiled to receive a desiredcharge of plastic explosive. The insert may comprise a plurality ofmembers, one of which may be located relative to the other after acharge of plastic explosive has been introduced into the first member.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example two embodiments of the invention will now be describedwith reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a section through a tube to tube plate joint and a part of anadjacent joint illustrating a first repair technique in accordance withthe invention, and

FIG. 2 is a similar section illustrating a second repair technique inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In both drawings the reference numeral 10 indicates a tube plate inwhich tubes 12 have been secured in respective openings. In FIG. 1, itis assumed that the joint between the tube and the tube plate was madeby a technique in accordance with our prior U.S. Pat. No. 3,503,110.Thus, each tube plate opening has a tapered portion at the front face ofthe tube plate, and each tube 12 originally extended through its openingto that front face. Assume now that a leak occurs in the weld at thetapered portion 14.

The first stage in the illustrated repair technique is to remove theoriginal portion of the tube welded to the tube plate on the taper 14,thereby exposing the tube plate surface on the taper. This can be doneby a suitable machining technique, in the course of which the taper onthe tube plate is continued across the end of the remaining tube portionas indicated at 16. The second step is to enlarge the bore of the tube12 within the tube plate 10, as illustrated at 18.

The device 20 shown in FIG. 1 is now located in the position shown inthat figure. The device comprises a connector 22, preferably of aductile metal, for example nickel. Connector 22 contains an insert 24 ofsolid energy transmitting material, preferably plastics such aspolyethylene. The insert has a bore comprising two portions 26, 28, thebore portion 28 being of larger diameter.

Connector 22 comprises five integral portions as follows, starting fromthe left-hand end of the connector as shown in FIG. 1:

(a) a cylindrical portion 30,

(b) a frusto-conical portion 32,

(c) a cylindrical portion 34,

(d) a frusto-conical portion 36,

(e) a cylindrical portion 38.

A detonator 40 is located within the insert 24 so that most of theelongate base charge 42 contained within the detonator case lies in thebore portion 26 of the insert, but a small length of the base chargeprojects into the bore portion 28 of the insert. The full length of thebore portion 28 is lined with a sleeve of a suitable explosive 44. Inuse, the detonator is initiated via leads 46, producing a detonationfront travelling from right to left through the base charge 42 as viewedin FIG. 1. The shock front produced by the explosive is transmittedthrough the insert 24 to expand the connector portions 32 and 30 intoengagement with the drilled out portion 18 of the tube 12. The amount ofmaterial removed from the tube 12 in the drilling operation is such thatthe original bore of the tube is substantially re-established by theexpanded surface of the connector 22, as can be seen from the completedrepair shown in the lower half of FIG. 1. Further, the choice ofexplosive for the detonator and the initial angle between thefrusto-conical portion 32 and the tube portion 18 is such that a weld isformed between the frusto-conical portion 32 of the connector and thetube portion 18, as described in our prior U.S. Pat. No. 3,503,110. Thelocation of this weld is indicated by the wavy interface shown at 48 inthe lower portion of FIG. 1.

Because of projection the charge 42 into the cylindrical charge 44, thelatter is initiated simultaneously, producing an annular detonationfront travelling from left to right through charge 44. The cylindricalportion 34 of the connector is therefore firmly expanded into contactwith the tube portion 18, and the frusto-conical portion 36 of theconnector is expanded into contact with the tapered end surface of thetube. The tapered surface on the tube provides a transition between thecylindrical surface of the tube 18 and the tapered bore 14 avoidingundue stress in the connector material in the transition region. Thecylindrical portion 38 of the connector is progressively expanded intocontact with the tapered bore 14 on the tube plate, forming a weldindicated by the wavy interface 50 in the lower half of FIG. 1. Thechoice of explosives and of angles required to produce such a weld isfully disclosed in our prior U.S. Pat. No. 3,503,110.

Thus, it will be seen from the lower part of FIG. 1 that the end portionof the tube 12 has been substantially reconstituted and rewelded to thetube plate 10 to provide a leak-tight joint, without substantialrestriction in the bore of the tube 12 but with a thinner tube end.

The arrangement shown in FIG. 2 is also designed to reconstitute the endof a tube and weld it to a tube plate in a leak-tight fashion. In thiscase, however, there is no tapered bore in the tube plate. The originaljoint could be made for instance by mechanical or explosive expansion toform a mechanical joint or by fusion welding at the front face of thetube plate or by explosive welding using a parallel geometry technique,for example as described in U.S. Pat. No. 3,409,969. The end portion oftube 12 is again removed to expose a surface of the tube plate withinthe bore, and the bore of the remaining tube end is again enlarged. Theexposed surface of the tube plate is indicated by the numeral 52, andthe drilled out portion of the tube is indicated by the numeral 54 inFIG. 2. In this case, a more complex connector 56, having the followingportions is required:

(a) a cylindrical portion 58,

(b) a frusto-conical portion 60,

(c) a cylindrical portion 62,

(d) a frusto-conical portion 64,

(e) a cylindrical portion 66,

(f) a frusto-conical portion 68, and

(g) a cylindrical portion 70.

The portions 58, 60, 62 and 64 correspond with the portions 30, 32, 34and 36 in FIG. 1 and function in the same manner. The portion 66 isarranged to engage the surface of the tube plate within the bore, andthe portion 68 is to be welded to the tube plate as will be describedbelow.

The connector 56 contains a tubular insert portion 72 of a materialsimilar to that described above for the insert 24. The insert portion 72has a bore comprising three sections, 74, 76 and 78 considered from theleft-hand end as shown in FIG. 2. Bore 74 is dimensioned to receive apredetermined weight per unit length of a given plastic explosive, forexample that sold by ICI under the name "Metabel". A column of suchexplosive is formed in the bore 76, leaving the right hand end of thebore free to receive one end of a detonator 80, the rest of whichprojects from the bore 74 into the left-hand end of the bore 76. Theremainder of the bore 76 is filled with plastic explosive. When the bore76 has been filled, a sleeve 82 of similar material to the insertportion 72 is located in the bore 78 and reduces the internal diameterof that bore to a predetermined value. The remaining bore is then alsofilled with a plastic explosive, the quantity of explosive thereforebeing determined by the bore of the sleeve 82.

Initiating wires 84 for the detonator extend through the sleeve 82. Whenthe detonator is initiated via those wires, a detonation front travelsfrom the detonator leftwards along the bore 74, causing expansion of theconnector portions 60 and 58 and welding of portion 60 to the drilledout tube 54; the resulting weld is shown in the wavy interface 86 in thelower part of FIG. 2.

The detonator also initiates the plastic explosive within the bore 76,causing a detonation front to travel rightwards along the explosivecolumn, as viewed in FIG. 2. This expands the connector portions 64 and66 into engagement with the tube end and tube plate surfacesrespectively, and causes progressive expansion of the connector portion68 against the tube plate to form a weld as indicated by the wavyinterface 88 in the lower half of FIG. 2. In both of the connectorsshown in FIG. 1 and FIG. 2, the cylindrical end portions 30, 58 and 70avoid premature dissipation of the expansion effect due to theexplosive, ensuring a weld over the full length of each taperedconnector portion 32, 60 and 68.

The invention is not limited to details of the illustrated embodiments.In FIGS. 1 and 2, both the weld with the tube plate and the weld withthe tube have been made within the tube plate bore, and this ispreferred because the tube plate itself supports the tube duringformation of a weld between the tube and the connector. However, if asuitable support can be arranged around the tube, a weld between thetube and the connector can be made outside the tube plate bore. Thislatter arrangement will be particularly useful where the tube was joinedto the tube plate by a weld at the back face of the plate, so that itdid not extend into the tube plate at all or to any significant extent.

In the illustrated embodiment, it has been assumed that welds are to beproduced by the techniques described in our prior U.S. Pat. No.3,503,110. However, this is not essential. Alternative explosive weldingtechniques, for example using parallel geometry, are known and examplesthereof have been cited in the introduction to this specification.Further, it may not be essential to form a welded joint at all, since amechanical expansion joint may prove sufficient. For example one form ofexpansion joint is shown in our prior British Patent Application18446/75.

Further, it has been assumed desirable to make both joints, that is thejoint with the tube and the joint with the tube plate substantiallysimultaneously. However, the joints could be made successively, in asingle operation but requiring only a single detonation front travellingin one direction through a column of explosive. In a furtheralternative, the two joints could be made in separate operations.However, this latter possibility is relatively cumbersome.

It will be appreciated that the invention enables tubes to be kept inservice even though the joint with the tube plate has deteriorated.Normally such tubes must be plugged off, for example as described in ourprior British Pat. No. 1 439 141. Also, if an end portion of the tubehas deteriorated, for example has been eroded as described in U.S. Pat.No. 3,781,966, the invention enables tube end replacement. Further, ifthe end portion of the tube has developed a leak separate from the jointbetween the tube and the plate, this leak can also be repaired by meansof a replacement tube portion as described above with the replacementtube portion either covering up the leaking tube portion or replacingit. The expression "repairing a joint" is therefore to be interpretedbroadly, and is not limited to repair of a leak in the joint itself. Inthis invention, however, the connector piece is connected to two bodies,even though leakage may appear in only one of them.

Where an end portion of the tube is severely eroded, it may not bepossible to remove all of the erosion marks by drilling out as describedabove. If remaining erosion marks are so deep as to endanger theconnector upon explosive expansion, the or each remaining mark may befilled before insertion of the connector. The filler material shouldprevent penetration of the connector into the erosion mark at least soas to avoid significant damage to the connector. Similar remarks applywhere a crack has appeared right through the wall of the tube causing itto leak in the joint region; such a leak can be repaired by replacingthe end portion of the tube by a technique as described above, with theconnector extending sufficiently far down the tube to close off theleak. The crack may have to be filled, however, as described above.

In the description of the drawings, we have referred to re-establishmentof the original tube bore. This is desirable, but it is clearly notessential. Even in the illustrated embodiments, we have not attempted tore-establish the original tube bore at the front face of the tube plate,where the connector is welded to the plate. The original tube bore couldbe re-established in that region by suitable adjustment of the wallthickness of the connector, but this will not be necessary in mostcases.

The frusto-conical portions 16 and 64 of the connector shown in FIGS. 1and 2 are desirable but not essential. Each limits the insertion of theconnector, simplifying the initial assembly operation. Further, theportion 64 gives extra room at the end of its connector for provision ofthe swaged down portion 68, while leaving adequate space within theconnector to receive both the insert and the charge.

We have referred above to production of the reduced diameter portions ofthe connectors by swaging. Alternative techniques are spinning,die-sinking, for example push-pointing, and rolling. The connector maybe formed around a preformed insert or may be formed separately from theinsert. In the latter event, a device as shown in FIG. 2 could beproduced by casting of the insert within the preformed connector.

In the illustrated arrangements the devices have been inserted so thattheir outer ends are substantially aligned with the front face of thetube plate. In many cases, it will be preferable to cause the outer endsof the connectors to project from the front face of the tube plate; theexpansion of the connector will then cause "cut-off" of the unsupportedends of the connectors at the front face; this facilitates a weld rightup to the front face of the plate avoiding a crevice at that face.

The repair technique is suitable for use on tubes originally secured byany of a wide range of different techniques; for exampleonly--explosively welded, fusion welded, explosively expanded to form amechanical joint, roller expanded.

I claim:
 1. A method of repairing a pre-existing joint between a tubeand a tubeplate of a heat exchanger, the tube extending through anaperture in the tubeplate and terminating adjacent to the surface of thetubeplate, comprising the steps of:(a) removing part of the length ofsaid tube within the confines of the tubeplate thereby leaving exposed apart of the length of the tubeplate wall defining said aperture; (b)locating an open ended tubular metallic repair member within said tubewith a part of the length of said member protruding from the tube towardthe surface of the tubeplate; (c) explosively radially expanding saidmember so as to form circumferentially continuous welds between theexternal surface of said member and, respectively, the interior of thetube and said exposed part of the wall defining the aperture in thetubeplate.
 2. A method as recited in claim 1 wherein step (b) ispracticed by:locating a first portion of the tubular repair memberwithin the tube and engaging the interior of the tube; locating a secondportion of the tubular repair member within the tube and so externallyshaped that there is a tapered annular space between it and the interiorof the tube; and locating a third portion of the tubular repair memberwithin the tubeplate aperture and so externally shaped that there is atapered annular space between it and the said exposed part of the walldefining the aperture; and wherein step (c) is practiced so thatexplosive expansion causes at least part of the second and thirdportions of the tubular repair member to become circumferentially weldedto the interior of the tube and tubeplate wall respectively.
 3. A methodas recited in claim 2 wherein step (b) is practiced so that the secondportion of the tubular repair member is disposed intermediate the firstand third portions thereof.
 4. A method as recited in claim 2 or 3wherein the third portion of the tubular repair member is cylindricaland extends to the adjacent end of the repair member, and wherein step(a) is practiced so that the exposed part of the wall defining theaperture tapers toward the tube.
 5. A method as recited in claim 1comprising the further step of, prior to step (b), counterboring thepart of the length of the tube surrounding the repair member, so thatafter radial expansion of the repair member, the repair membersubstantially re-establishes the original tube bore.
 6. A method asrecited in claim 1 wherein steps (a) through (c) are practiced so thatthe weld between the external surface of the repair member and theinterior of the tube is at least partially within the confines of thetubeplate.